Many of us who reject claims about the supernatural do so on the grounds that extraordinary claims require extraordinary evidence. But this may be a source of confusion, depending on what the word extraordinary means.
A claim about the supernatural is extraordinary, which means outside or beyond the ordinary. Claims about nature and history are ordinary, because we make and believe them all the time, and we have agreed standards of evidence to assess them if we need to. And different claims require different kinds and amounts of evidence.
But the only standards of evidence we have are for ordinary claims about nature and history. We have no standards of evidence for claims about the supernatural. So to say we want extraordinary evidence for such claims could be a mistake. We have no way to assess such evidence.
And this mistake can lead to the idea that we can’t assess claims about the supernatural, because we have only standards of evidence for claims about nature and history. And this is a get-out that many who make and believe claims about the supernatural actually use.
To assess claims about the supernatural, what we really need is not extraordinary evidence, but rather very convincing ordinary evidence – of which there has been none so far.
My new formulation is: extraordinary claims require ordinary evidence that's extraordinarily convincing.
Any ideas to improve it are most welcome, and I’ll acknowledge helpful suggestions.